Problem: Valid Palindrome

Given a string, s, return TRUE if it is a palindrome; otherwise, return FALSE.

A phrase is considered a palindrome if it reads the same backward as forward after converting all uppercase letters to lowercase and removing any characters that are not letters or numbers. Only alphanumeric characters (letters and digits) are taken into account.

Constraints:

• $1 \leq$ s.length $\leq 3000$

• s consists only of printable ASCII characters.